By the end of the 17th century, the growing British iron industry was facing several crises which threatened its prosperity. The resolution with which the industry faced these challenges sparked the innovations that took place in the 18th century, completely transforming the industry itself and launching the Industrial Revolution.
England had iron ore in abundance and at shallow depths. However, because it was not yet technically possible to remove all impurities, English Bar Iron was inferior to that made from certain ore bodies outside of Britain which had fewer impurities. In the early 1700s, 2/3 of the Bar Iron used by the British iron industry was imported mainly from Sweden but also from Russia and America. Political events periodically disrupted these sources and England frequently found her foreign policy affected by her dependence on these sources.
Smelting and refining the ore required enormous amounts of charcoal. Early on this was not a problem as England was heavily forested, but by the 17th century the iron industry and the Navy were in competition for the remaining woodlands. As charcoal shortages became acute and the price rose alarmingly.
A reliable source of swiftly running water was essential for the power to run the bellows, the hammers and the slitting machines. In times of drought the works had to pump water back up to reservoirs to be used again. When the rivers froze, the works had to close down.
Over the previous century, the British iron industry had initially responded to these challenges by specialization and by dispersal. Small enterprises conducting one aspect of the process were located near their most needed resource and in turn supplied their product to another company specializing in the next step in fabrication. For instance, the wooded Forest of Dean area specialized in charcoal smelting and supplied Pig Iron to forges and foundries. Black smiths would locate near a source of the coal which they used to fire their forge and would supply the immediate neighborhood with Bar Iron slit into small rods suitable for home industries such as nail making.
However, the most urgent problem by far was the industry’s voracious appetite for wood to make the charcoal which was essential to the smelting and refining process known at that time. Parliament, concerned about the rapid disappearance of a resource vital to the Navy, passed several Acts preventing the cutting of woodlands to make charcoal. The rising price of charcoal meant the price of British iron products was not competitive with imported iron wares. It was imperative that the iron industry find a way to use an alternative fuel such as peat or coal, both of which were plentiful.
Peat is very flammable and burns quickly and dangerously hot. The most promising fuel seemed to be coke (which is coal burned in an oxygen deprived atmosphere to concentrate its carbon), but coke contributed its own impurities - such as sulphur - which produced inferior Pig Iron. One could not use brittle coke Pig Iron to cast such things as plowshares and anchors which must be able to weather hard knocks. Worse, it seemed impossible to turn coke Pig Iron into the malleable Bar Iron needed to make wrought iron at the forge.
Abraham Darby of Shropshire approached the problem by concentrating on finding a better way of making coke in order to first eliminate the impurities in the fuel itself. Using the “sweet” clod coal of the district, he finally succeeded in making commercially acceptable Pig Iron using coke in his blast furnace at Coalbrookdale in 1709. He also built a larger blast furnace which achieved a higher temperature over a longer period of time thereby achieving a more complete fusion of the carbon coke and the iron. This produced a purer, more liquid metal that could fill all the tiny cavities of a mold and resulted in a superior casting.
By the 1750’s new coke furnaces were being put into blast throughout the country. Higher temperatures were being achieved by greatly accelerating the blast of air fanning the fires at first with Smearton’s blowing cylinders and later in the 1760’s by James Watt’s even more successful double acting steam engine to accomplish a more complete fusion. Coke Pig Iron was now good enough for all general purposes either as wrought or cast iron. However, charcoal was still used in the last step to create Bar Iron.
In 1784 Henry Cort introduced his “puddling” process which involved heating the Pig Iron in a hot air Reverberatory Furnace (which kept the iron separate from and unpolluted by the coke) that could maintain the molten iron at welding temperature while it was being stirred with paddles before being passed through rollers. The combination of the high temperatures and the physical manipulation of the iron eliminated all the dross and altered the molecular structure without the use of charcoal. The resulting iron was superior to Swedish Bar Iron and suitable for all purposes except for making steel. It was a faster process and cheaper than charcoal Bar Iron by half since it used only coke. This was a break-through of huge significance.
“… (Cort’s) discovery was one of the outstanding events in the history of technology”. (The Industrial Revolution, T.S.Ashton p. 55)
Ashton lists the beneficial consequences: it brought the forge and the foundry sides of the industry together in one vertically integrated business; it liberated Britain from her dependence on foreign Bar Iron; it led to an expeditious growth of the British iron industry; ” …and there was hardly an activity – from agriculture to ship-building, from engineering to weaving – that did not experience the animating effects of cheap iron”. (Ibid p. 54-55)
By the 1790’s the British iron industry had solved its power problems by employing Watt’s steam engines to neutralize the fickleness of water power; it had solved the critical charcoal shortage by developing ways to use plentiful coke as fuel; it had eliminated the need to import Bar Iron by developing a method to refine British ores to an even superior level of quality and it had done all this while greatly lowering the manufacturing costs. The industry was poised for an explosion of innovation and expansion. The Darby and Wilkinson clans and their industry colleagues were of the mind that there was nothing that could not now be made of iron.